Compounds containing the butenolide ring which has the basic formula: ##STR1## occur widely in nature and often possess an unusual range of biological activities. They appear throughout the plant kingdom from the simple metabolites of lichens, mold and fungi, to the more complex sesquiterpenes of the family Compositae and steriodal glycosides of the families Ranunculaceae, Liliaceae, Scrophullariaceae, and Apocyanaceae. More recently butenolides have been observed in such diverse animal species as sponges, and insects. In the latter species they may play a significant role as chemical defense weapons.
Certain butenolide ring containing compounds are useful as insecticides, herbicides, and seed and plant growth regulators. Of considerable importance also is the widespread characteristic among butenolide containing compounds of allergenic, antibacterial, and antifungal activity.
Undoubtedly, Vitamin C is the most physiologically important butenolide ring containing compound. Other uses for certain butenolide ring containing compounds include recently reported uses of cardiac glycosides as having the unusual characteristics of reducing the frequency of the heartbeat but increasing the amplitude of the heartbeat.
The unusual range of usefulness of compounds containing the basic butenolide ring has stimulated considerable research on the synthesis of these valuable compounds. While numerous methods have been reported in the literature for the preparation of butenolides, see for example, Y. S. Rao, Chem. Rev. 64, 353 (1964); W. E. Epstein and A. C. Sonntag, J. Org. Chem., 32, 3390 (1967); K. Iwai, M. Kawai, H. Kosugi and H. Uda, Chem. Lett., 385 (1974); and K. Iwai, H. Kosugi and H. Uda, Chem. Lett., 1237 (1974), these methods all generally suffer from several disadvantages. Some of these disadvantages include inaccessibility of the starting materials, the necessity for employing severe reaction conditions, the very low yields of product obtained, and generally limited versatility in preparing the desired butenolide ring containing compounds.
The major objectives of the process of my earlier filed application, Ser. No. 616,436, were to provide a general synthesis route for a wide variety of butenolide compounds, to avoid the use of hydrogenation techniques and Grignard reagents, to provide a convenient two step synthesis for .beta.-halobutenolides and to provide a process which provided high yields of the desired butenolides.
The reaction provided in my earlier invention could be conducted either in the presence of reaction equivalent amounts of noble metal salts or in the presence of catalytic amounts of noble metals.
It has now been found that the process of my earlier invention can be improved, from the standpoint of yield, particularly where the catalytic addition reaction is employed; and particularly where the trans-vinyl mercuric halide, employed in the second step reaction has a secondary or tertiary alcohol substitution, as distinguished from use of simple propargyl alcohol to prepare a trans-vinyl mercuric compound wherein R and R' are hydrogen, and the alcohol is therefore a primary one.